1. Field of the Invention
The present invention relates to a method and apparatus for efficiently and simply separating a membrane from the inside of egg shells, and, in particular, a method and apparatus for separating a protein membrane from waste egg shells.
2. Description of the Related Art
Nearly 30% of all eggs consumed today in the United States are used to manufacture processed egg products that are used as ingredients in other processed foods and various food service operations. For example, the albumen (“egg white”) and egg yolk may be recovered to manufacture liquid egg products of various types. In other instances, the albumen and egg yolk may be dried to form a more shelf-stable product (e.g., powdered eggs).
The use of eggs by the processed egg sector of the industry is increasing markedly, according to the United States Department of Agriculture. In 1984, the egg processing industry utilized 25.6 million cases of eggs to manufacture liquid and dry egg products. In 1995, 47.5 million cases of eggs were utilized. Estimates for 1997 indicate that more than 50 million cases of eggs were utilized in a variety of further processed egg products.
The waste egg shells amassed from such processing are usually subjected to further processing (e.g., such as with a centrifuge) in order to recover residual albumen which adheres to the egg shells, which can be sold to the pet food industry. Nevertheless, the egg shells, whether further processed or not, are largely disposed of as a waste product.
Based on 1997 estimates, therefore, more than 120,000 tons of unprocessed egg shell waste were generated. More specifically, a survey conducted in collaboration with the United Egg Producers indicated that almost 50% of U.S. egg producers each generate 1000 to 3000 tons of egg shell waste each year. Among the survey respondents, 26.6% used the egg shell waste as fertilizer, 21.1% used it as a feed ingredient, 26.3% disposed of it in dumps as waste, and 15.8% put it to “other” use(s). Among the respondents identifying disposal costs, almost three-quarters reported disposal costs between $25,000 and $100,000 per year. In view of the significant disposal costs for what is conventionally totally a waste product, and additionally, in view of current environmental practicalities which are decreasing the availability of local disposal sites (thereby further increasing disposal cost), it will be readily appreciated that finding a significant use for egg shell waste would have important financial and environmental, benefits.
It is well-known that the egg shell of a chicken, comprises an inorganic external mineral portion and an internal organic matrix upon which the mineral portion is built. The mineral portion is primarily calcitic calcium carbonate. The organic matrix generally comprises an inner and outer membrane layer, each of which are comprised of a network of proteinaceous fibers, upon which the mineral portion of the shell is formed.
The presence of hydroxyproline in hydrolsates of the membrane layers suggest that the membrane layers include collagen as a component of the fiber structure. Biochemical and immunological testing has confirmed this. It has been established that of the total proteinaceous content of the membrane structure of an egg shell, about 10% is collagen.
Moreover, genetic collagen variants have been identified in the shell membranes, with the outer shell membrane being predominately type I and the inner shell membrane being types I and V. In addition, type X collagen has been found in both the inner and outer shell membranes through immunohistochemical analysis. It is important to recognize the presence of collagen in eggshell membranes because of its potential monetary value.
The presence of collagen in the shell membranes is interesting because of the increasing demand for collagen. Bovine, and to a lesser extent, human, collagen is becoming relatively commonly used in a variety of applications, especially in the biomedical field. For example, a collagen glue made from human collagen is known for filling corneal wounds. Also, research in ongoing in producing skin and tissue replacement products made from collagen. Unfortunately, the cost of such collagen based products is very high (at least about $1,000 per gram, or about $454,000 per pound), although such costs are considered economically acceptable, at least in medical applications, in view of the overall cost of medical treatment.
Based on estimates for 1997 egg consumption, as discussed above, approximately 120,000 tons of egg shell waste would yield 110,000 tons of egg shell and 10,000 tons of membrane. Taking into account that about 10% of the membrane is collagen, this would yield 1,000 pounds of collagen.
In addition, use of bovine collagen raises an issue as to the possible transmission of bovine spongiform encephalopathy (commonly known as “mad cow disease”). Although, as a practical matter, the risk of mad cow disease transmission is very small, the mere perception of possible risk creates a need for private, well-isolated, and expensive herds.
Another problem with bovine collagen is the risk of autoimmune and allergic reactions caused thereby, since approximately 2% to 3% of the population is allergic in this regard. Although, this would appear to be a small percentage, the problem is likely to increase as the use of bovine collagen products becomes more common.